This invention relates in general to the mixing of chemical solutions and deals more particularly with a tumbling machine which is used to simultaneously mix the contents of a plurality of glassware containers.
Various types of chemical solutions must be throughly mixed in order to permit analysis of the contents. For example, devices known as block digesters are used in analyzing feed samples and fertilizer samples which are reacted and mixed in volumetric glassware tubes with chemicals such as sulphuric acid solutions and then brought to a specific volume. The volumetric tubes are held in the block digester in a rack which typically supports 20 or 40 individual tubes. After the racks are removed from the block digester, the chemical solutions in the tubes must be throughly mixed so that the chemical analysis can proceed.
At present, mixing of the solutions is normally carried out manually by shaking each individual volumetric tube in the hand. As can easily be appreciated, this manual mixing operation is an unpleasant task which takes considerable time and effort on the part of laboratory technicians. Also, because the solutions usually contain acids and other volatile substances, the workers are exposed to the possibility of chemical burns. It has been found that a relatively slow rate of rotation of the tubes on the order of six revolutions per minute results in the most effective mixing for the types of solutions which are contained in block digestion tubes. The slow rate of rotation effects thorough mixing primarily because air bubbles in the tubes can then reciprocate the full length of the tube to facilitate mixing of dense substances with lighter substances. It is difficult at best to achieve such a slow rate of rotation manually, and even if it is achieved, the valuable time of laboratory technicians is consumed. A further drawback in connection with the manual mixing operation is that it cannot be accurately timed to continue for the proper length of time. If the solutions are mixed for too short a period, they are not mixed throughly enough and if they are mixed too long, time is wasted needlessly and the chemical analysis is delayed.
The present invention is aimed at eliminating these problems and has, as its principal object, the provision of a mixing machine for automatically mixing various types of chemical solutions contained in volumetric glassware containers. The automatic operation of the machine is of particular importance because it permits the contents of the containers to be mixed unattended, thus freeing the laboratory technicians for more productive work during the mixing operation. Additionally, the unpleasant task of manually mixing the tubes is eliminated.
Another important object of the invention is to provide a mixing machine of the character described which orients each of the volumetric tubes in an upright position after completion of the mixing operation.
A further object of the invention is to provide a mixing machine of the character described which tumbles the volumetric tubes at a constant rotational speed which is relatively slow in order to effectively mix the solutions contained in the tubes.
Still another object of the invention is to provide a mixing machine of the character described in which the mixing time can be accurately preset and can be adjusted as desired throughout a wide range.
An additional object of the invention is to provide a mixing machine of the character described wherein leakage from the glassware tubes is prevented and the tubes are held against shifting movement in the tumbler. The tumbler is constructed to hold the glassware tubes firmly between the lid and floor with the lid of the tumbler bearing against stoppers which are fitted in the tubes to seal their open top ends against leakage.
Yet another object of the invention is to provide a mixing machine of the character described which is well adapted to accomodate glassware tubes of various sizes and styles and various types of racks.
A still further object of the invention is to provide a mixing machine of the character described which is simple and economical to construct and safe and reliable in operation.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.